Ecosystem comparisons of oasis lakes and soils
Terrestrial biology Ecosystem comparisons of oasis lakes and soils G. M. SIMMONS, JR., B. C. PARKER, F. C. T. ALLNUTT, D. P. BROWN, D. D. CATHEY,
and
K. G.
SEABURG Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061
During the 1978-79 field season, the ecosystem comparisons of oasis lakes and soils (EcoLs) project followed up on last season's preliminary studies of ten lakes among the unusual and highly diverse lake ecosystems located within a relatively small area of about 3,000 km2 in southern Victoria Land. Focusing on Lakes Fryxell and Hoare, we used the wide variety of limnological methods described earlier (Parker and Simmons, 1978) and also used a team of research divers to make the first direct underwater observations and sampling of benthic algal mats. The general objectives of the ECOLS project are to understand the interactions between dry valley (or oasis) lakes and their associated soil and glacial meltstream in puts and to assess the mechanisms by which the biotic communities have evolved in these arheic (i.e., nonoutflowing) antarctic lakes. The first ECOLS season indicated that the plankton community of Lake Fryxell was the most productive and that of Lake Vanda the least productive in terms of carbon-14 measured photosynthesis, extractable chlorophyll a, adenosine triphosphate, and community diversity. Lakes Bonney, Joyce, Miers, and Hoare, in that order, fell between Lakes Fryxell and Vanda. The second field season has confirmed that, while seasonal and depth variability in numerous measurements occurs, Lake Fryxell consistently remains more productive than Lake Hoare. The list of selected measurements from these two lakes in the accompanying table documents this point. Much more data are now being interpreted. The maximum depth of attached blue-green algal mat communities in highly oxygenated Lake Hoare remains obscure, but we do know that the anaerobic, sulfide-rich layer below 10-11 meters is the limit for blue-green algal mats in Lake Fryxell. Of considerable interest is the observation that well-developed mat communities in Lake Hoare occur at the peizometric depth of about 8 meters, where the light intensity is equal to or less than 1 percent of the photosynthetically available surface radiation.
This presence of well-developed algal mats at low light levels is even more unusual when one recognizes that this lake receives no light for at least 4 months during the antarctic winter and very little or no light during most of the remaining months of the year. Thus, the chromatic adaptive capability of these deep benthic attached algae may reach a maximum in this type of lake. Two years of data on orthophosphate concentration levels and phosphorus-33 uptake experiments have demonstrated that phosphorus is a major limiting nutrient to the plankton of these southern Victoria Land lakes. This degree of limitation appears to follow the order: Lake Vanda = Joyce > Hoare > Bonney (west lobe) > Fryxell > Miers. Only in the monimolimnia of Lakes Fryxell and Bonney were phosphorus levels detectable by direct wet chemical analysis. In every lake studied, the Km + P0 data greatly exceeded the ambient concentrations of dissolved phosphorus, which means that phosphorus would be taken up at greater velocities whenever it became available. The mathematical model for Lake Bonney also predicted that phosphorus was limiting. Acetylene reduction was significant in shallow and moat water blue-green algal mats of Lakes Chad and Fryxell and the blue-green algal communities in peripheral waters of Lakes Hoare and Fryxell. The dominant blue-green algae in those shallow and peripheral water mats are heterocystous species (figure 1). In contrast, no conclusive acetylene reduction was detected in mats taken from deeper waters beneath the ice of these lakes. The deeper water mats also lacked heterocystous bluegreen algae, consisting primarily of Oscillatoria, Phormidium, and/or Schizothrix spp. Although there is limited ammonium and nitrate ion concentration data, it is clear that nitrogen fixation and
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Figure 1. Anabaena sp. with heterocysts and developing akmetes, while actively fixing nitrogen In Lake Hoare, southern Victoria Land (approximately 188 x). 181
Table 1. Data for select measurements during 1978-79 austral summer for Lakes Fryxell and Hoare * Lake Fryxell Lake Hoare
Measurement Water Column Adenosine Tnphosphate (Extractable, ng 11) Overall Range Detected Season's Range for Means of All Water Samples for Given Sample Dates Chlorophyll a (Extractable, 1Lg 11) Overall Range Detected Season's Range for Means of All Water Samples for Given Sample Dates Ammonium Nitrogen (AM, as NH4-N) Range with Depth and from Habitat-to-Habitat Nitrate Nitrogen (SM, as NO3-N) Range with Depth and from Habitat-to-Habitat Detectable Significant Nitrogen (C21-12)-flxing Activity Shallow Moat or Peripheral Water Mats (Anabaena in Hoare; Nostoc Deep Water Mats Beneath Permanent Ice (No Heterocystous Blue-green Algae; only Oscillatonaceae) Dissolved Silicate Range (SM, as Si(OH)4) Orthophosphate-P (LM, as PO4-P)
3 -435 1 -69 29 -123 3 -49 0.3 -18 4 -7
0.02-5 0.2 -4
0.26-0.51 0.31-6.1 0 -0.32 0.34-2.5 +
+
±
-
11 -69 10 -130 0 0 (except 1-2 in monimolimnion)
* Lake Chad, which has extensively developed, attached heterocystous blue-green algal mats, also showed significant acetylene reduction.
the presence of heterocystous species occurred in every case where there was little available fixed nitrogen (
and
K. G.
SEABURG Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061
During the 1978-79 field season, the ecosystem comparisons of oasis lakes and soils (EcoLs) project followed up on last season's preliminary studies of ten lakes among the unusual and highly diverse lake ecosystems located within a relatively small area of about 3,000 km2 in southern Victoria Land. Focusing on Lakes Fryxell and Hoare, we used the wide variety of limnological methods described earlier (Parker and Simmons, 1978) and also used a team of research divers to make the first direct underwater observations and sampling of benthic algal mats. The general objectives of the ECOLS project are to understand the interactions between dry valley (or oasis) lakes and their associated soil and glacial meltstream in puts and to assess the mechanisms by which the biotic communities have evolved in these arheic (i.e., nonoutflowing) antarctic lakes. The first ECOLS season indicated that the plankton community of Lake Fryxell was the most productive and that of Lake Vanda the least productive in terms of carbon-14 measured photosynthesis, extractable chlorophyll a, adenosine triphosphate, and community diversity. Lakes Bonney, Joyce, Miers, and Hoare, in that order, fell between Lakes Fryxell and Vanda. The second field season has confirmed that, while seasonal and depth variability in numerous measurements occurs, Lake Fryxell consistently remains more productive than Lake Hoare. The list of selected measurements from these two lakes in the accompanying table documents this point. Much more data are now being interpreted. The maximum depth of attached blue-green algal mat communities in highly oxygenated Lake Hoare remains obscure, but we do know that the anaerobic, sulfide-rich layer below 10-11 meters is the limit for blue-green algal mats in Lake Fryxell. Of considerable interest is the observation that well-developed mat communities in Lake Hoare occur at the peizometric depth of about 8 meters, where the light intensity is equal to or less than 1 percent of the photosynthetically available surface radiation.
This presence of well-developed algal mats at low light levels is even more unusual when one recognizes that this lake receives no light for at least 4 months during the antarctic winter and very little or no light during most of the remaining months of the year. Thus, the chromatic adaptive capability of these deep benthic attached algae may reach a maximum in this type of lake. Two years of data on orthophosphate concentration levels and phosphorus-33 uptake experiments have demonstrated that phosphorus is a major limiting nutrient to the plankton of these southern Victoria Land lakes. This degree of limitation appears to follow the order: Lake Vanda = Joyce > Hoare > Bonney (west lobe) > Fryxell > Miers. Only in the monimolimnia of Lakes Fryxell and Bonney were phosphorus levels detectable by direct wet chemical analysis. In every lake studied, the Km + P0 data greatly exceeded the ambient concentrations of dissolved phosphorus, which means that phosphorus would be taken up at greater velocities whenever it became available. The mathematical model for Lake Bonney also predicted that phosphorus was limiting. Acetylene reduction was significant in shallow and moat water blue-green algal mats of Lakes Chad and Fryxell and the blue-green algal communities in peripheral waters of Lakes Hoare and Fryxell. The dominant blue-green algae in those shallow and peripheral water mats are heterocystous species (figure 1). In contrast, no conclusive acetylene reduction was detected in mats taken from deeper waters beneath the ice of these lakes. The deeper water mats also lacked heterocystous bluegreen algae, consisting primarily of Oscillatoria, Phormidium, and/or Schizothrix spp. Although there is limited ammonium and nitrate ion concentration data, it is clear that nitrogen fixation and
-
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$
9
H
Figure 1. Anabaena sp. with heterocysts and developing akmetes, while actively fixing nitrogen In Lake Hoare, southern Victoria Land (approximately 188 x). 181
Table 1. Data for select measurements during 1978-79 austral summer for Lakes Fryxell and Hoare * Lake Fryxell Lake Hoare
Measurement Water Column Adenosine Tnphosphate (Extractable, ng 11) Overall Range Detected Season's Range for Means of All Water Samples for Given Sample Dates Chlorophyll a (Extractable, 1Lg 11) Overall Range Detected Season's Range for Means of All Water Samples for Given Sample Dates Ammonium Nitrogen (AM, as NH4-N) Range with Depth and from Habitat-to-Habitat Nitrate Nitrogen (SM, as NO3-N) Range with Depth and from Habitat-to-Habitat Detectable Significant Nitrogen (C21-12)-flxing Activity Shallow Moat or Peripheral Water Mats (Anabaena in Hoare; Nostoc Deep Water Mats Beneath Permanent Ice (No Heterocystous Blue-green Algae; only Oscillatonaceae) Dissolved Silicate Range (SM, as Si(OH)4) Orthophosphate-P (LM, as PO4-P)
3 -435 1 -69 29 -123 3 -49 0.3 -18 4 -7
0.02-5 0.2 -4
0.26-0.51 0.31-6.1 0 -0.32 0.34-2.5 +
+
±
-
11 -69 10 -130 0 0 (except 1-2 in monimolimnion)
* Lake Chad, which has extensively developed, attached heterocystous blue-green algal mats, also showed significant acetylene reduction.
the presence of heterocystous species occurred in every case where there was little available fixed nitrogen (
